The invention relates to fuel cells and, more particularly, to a solid oxide fuel cell (SOFC) system and process which is useful in connection with aircraft applications and jet fuel.
Fuel cells are a desirable alternative for use in generating electric power from hydrocarbon-based fuels more efficiently than a turbine based technology. The other advantages of having a fuel cell power the aircraft systems include, beneficial replacement of a gas turbine auxiliary power unit, reduction in the size of the main engines, reduction in emissions due to fuel cells being a cleaner technology, and reduced noise in airports due to comparatively lower number or size of rotating parts. In the case of the SOFC, the solid state technology and lower velocities of the fluid flow aid in lower noise.
Fuel cells are being considered as alternative generators for power for various applications, including power plants, motor vehicles and the like due to the higher efficiency of electrical conversion from the chemical energy of fuels like hydrogen, hydrocarbons, etc. Furthermore, it is established to be cleaner, environmentally friendly technology.
One such application is in aircraft, but use of fuel cells in aircraft applications has several advantages and disadvantages. The advantages are more efficient electrical energy generation, lesser emissions and lower noise signature. The disadvantages are the fuel cell systems tend to be heavier than their counter part gas turbine systems, with the current state of art, partly due to the need for fuel desulfurization and reformation prior to fuel cell stack input. The balance of the plant of the SOFC systems can also contribute to the weight. Additionally, the requirements for power conditioning increase the weight of the overall fuel cell based power generation unit. The other penalties of having a solid oxide fuel cell system in an aircraft may include increased drag caused by drawing air from outside, or loss in thrust due to use of air from cabin.
Jet A fuel is a typical fuel for use in aircraft applications. However, such fuel is not easily used in a fuel cell environment due to higher sulfur content and being a mixture of hydrocarbons with greater than 90% having more than 5 carbon atoms. Larger hydrocarbon molecules are not easily processed in a fuel cell, may lead to coke formation and need reformation to methane, carbon monoxide and hydrogen, which can be processed by SOFC thus minimizing the number of fuel processing reactors.
Further, in aircraft applications, redundant systems are desirable for obvious reasons.
Tight, technically sound, and beneficial integration of SOFCs into an aircraft application is therefore desirable, and is the primary object of the present invention.
It is another object of the present invention to provide a fuel cell system for aircraft applications which is effective with jet fuel, and which is efficient and reliable.
Other objects and advantages of the present invention will appear herein below.